1. Field of the Invention
The present invention relates to a filter apparatus, which is to be used in combination with a canister for removing toxic substances from a vaporous fuel generated in a fuel tank or the like for an internal combustion engine.
2. Description of the Related Art
A vaporous fuel generated in a fuel tank mounted on a vehicle contains substances, which is harmful to an environment. Such a vaporous fuel should therefore not be discharged into the atmosphere without being subjected to a specific treatment. There has conventionally been taken a countermeasure of provision of a canister receiving adsorbent such as an activated carbon or the like and connected to a generation route of the vaporous fuel so as to remove the toxic substances from the vaporous fuel by means of the canister to obtain a clean air and then to discharge the thus obtained clean air into the atmosphere.
The vaporous fuel is not always introduced into the above-mentioned canister. When the pressure of the fuel tank becomes for example negative, the canister sucks in air. The sucked air and substances adsorbed by the adsorbent are mixed and then returned to a fuel system. When the air sucked by the canister contains foreign matters, the foreign matters may be accumulated in the canister, thus deteriorating its performance. In view of these problems, a filter apparatus is connected to the outlet portion of the canister, which communicates with the atmosphere.
As the filter apparatus for a canister, there has conventionally been used a filter apparatus as shown in FIG. 8. The filter apparatus 1 is provided with a housing 2 made of synthetic resin, a filter element 3 received in the housing 2 and a one-way valve 4 for opening or closing a passage, which can bypass the filter element 3. Air discharged from the canister (not shown) is introduced into a connection-opening portion 2a of the housing 2. Fluid introduced into the connection opening portion 2a opens the one-way valve 4 to enter a valve chamber 2b. The fluid in the valve chamber 2b is then discharged through an element chamber 2d and an atmospheric release-opening portion 2e into the atmosphere. When the pressure at the side of the canister becomes negative, air is sucked from the atmospheric release-opening portion 2e of the housing 2 into the element chamber 2d. The thus sucked air is filtered through the filter element 3 and then introduced into the canister through the connectionopening portion 2a.
According to the above-described filter apparatus 1, the air discharged from the canister bypasses the filter element 3 and discharges into the atmosphere, thus leading to the maintenance of a small exhaust resistance. The air sucked into the canister is securely filtered through the filter element 3 on the other hand.
However, in the conventional filter apparatus 1 described above, the passage for discharging the fluid supplied from the canister and the passage for the air filtered through the filter element 3 are separated from each other at the region of the connection opening portion 2a. Such a structure requires the other valve chamber 2b provided other than the element chamber 2d, resulting in a complicated structure of the housing 2 and leading to increase in number of components. As a result, there take place an unavoidable increase in time and effort spent on manufacturing processes and assembling processes of the apparatus as well as an unavoidable increase in manufacturing costs due to the former.